Several New Methods of Reinforcement and Transformation of Old Wharf

1. Application of traditional structural reinforcement methods in wharf reconstruction

Most of the old piers on both sides of the Huangpu River in Shanghai Port were built in the 1980s and have now entered the maintenance period. Moreover, the damage of the wharf varies with the structure of the wharf, such as: cracks, steel corrosion, concrete carbonization, etc. The traditional reinforcement method is usually to dismantle the old superstructure of the wharf that does not meet the larger load-bearing requirements, use the original pile foundation, or properly reinforce the pile, and pour the upper concrete structure. The cast-in-place beams, prefabricated longitudinal beams and panels are used to form a whole through the cast-in-place surface layer. Although this transformation method can improve the current condition of the wharf and restore the carrying capacity of the wharf, it has a greater impact on the loading and unloading production of the port area. It is manifested as complex construction conditions and restricted construction space. For example, taking a high-piled wharf as an example, the damage is mainly below the wharf surface, and the reinforcement work must be built on the water platform, resulting in a narrow working surface, mechanized construction is not possible, and work efficiency is reduced. Moreover, compared with other reconstruction methods, the maintenance cost is relatively high, which is manifested in the poor construction environment. Since it is carried out in the port area, it will inevitably be affected by other berth operations. The movement of construction vessels and the layout of construction machinery will increase management costs. These factors will be reflected in the maintenance cost. Therefore, this method is difficult to meet the needs of loading and unloading production tasks in the old port area.

2. Application of structural bonding steel technology in wharf reconstruction

In view of the busy loading and unloading tasks of the wharf berths and the partial damage of the wharf beams and columns, the introduction of high-tech structural steel bonding professional technology to restore the wharf carrying capacity. Structural bonding steel reinforcement is a reinforcement technology for building structural engineering. Use a special structural adhesive to paste the steel plate on the surface of the reinforced concrete structure, so that the steel plate and the concrete component work together to achieve the purpose of strengthening and enhancing the strength and rigidity of the original structure.

Construction technology and operation requirements of bonded steel reinforcement:

1) First, repair the cracks on the concrete surface to form a seal. Then the surface of the concrete to be pasted is roughened, after removing the surface dirt and dust, wipe it with acetone.

2) Then derust and polish the sticking surface of the steel plate, and wipe it clean with acetone.

3) Configure the structural adhesive and curing agent in a ratio of 4:1, and stir until there is no color difference, no bubbles, and fully uniform structural adhesive.

4) Spread the configured structural glue evenly on the steel plate and concrete surface to be pasted, then paste the steel plate on the concrete surface, and fix the pressure with expansion bolts and angle irons through the reserved holes.

5) Finally, apply anti-rust paint on the surface of the steel plate.

The reinforcement and renovation project of Shanghai Port Gongqing #1—Cun 3 Berth Wharf, built in the early 1980s, adopted the bonding steel technology. The wharf is a high-piled beam slab structure. Due to various reasons such as natural aging of the concrete structure, uneven settlement, and improper use and management, some concrete components are damaged to varying degrees. Especially the beams of the wharf have cracks in many places. It can be seen from the investigation that the maximum crack width of the beam has exceeded the allowable value for normal use requirements specified in the code. Considering that the load will increase in the future, the foundation deformation, and the carbonization and shrinkage of the beam concrete may continue to expand the crack width. Therefore, in order to restore the carrying capacity of the wharf, the wharf must be transformed. After testing and reinforcement of the wharf beams, if the bonding steel technology is used, the load-bearing capacity of the beams can be restored, and the wharf can still meet the requirements of design bearing capacity and specifications. Therefore, the steel-bonded reinforcement method is used to stick the steel plate to the parts that need to be reinforced with an adhesive to restore the structural bearing capacity. Judging from the current use situation, the effect of the externally attached steel plate to restrain the generation of cracks and limit the propagation of cracks is obvious. However, because the pasted steel plate is in the water level fluctuation area for a long time, it is necessary to frequently strengthen the repair and maintenance of the steel plate.

3. Application of carbon fiber (CFRP) reinforced concrete technology in wharf reconstruction

Carbon fiber cloth reinforcement and repair structure technology is a new type of structure reinforcement technology popularized and applied in recent years. It uses resin bonding material to stick carbon fiber cloth on the surface of the concrete component, and uses the good tensile strength of the carbon fiber material to achieve the purpose of enhancing the bearing capacity of the component.

Shanghai Port Baoshan Port Co., Ltd. used this process method in the reconstruction project of the #6 and support 7 berths. The wharf is a high-piled beam slab wharf designed and constructed in the late 1980s. #6 berth is a general cargo terminal with a length of 180m, and #77 white berth is a river barge wharf, with a length of 90m and a width of 16m. The original design gantry crane has a lifting capacity of 10t, which meets the requirements of the development of container loading and unloading production. Use a door crane with a lifting capacity of 40t. After design, the internal force and structural strength of the rail beams, beams, and foundation piles of the wharf are checked separately. Under the premise that the wharf structure is intact, berths #6 and #7 can use customized 40t non-standard portal cranes. From the investigation, a small number of components at the front of the wharf are damaged by the impact of the ship, and all the longitudinal beams are intact. The main problem is that the lower beam under the front door beam is above the diagonal pile of the half-fork pile, and there is generally a perpendicular to the diagonal pile. Oblique cracks, more cracks in the lower beam extend from both sides to the bottom of the beam. The crack width with severe damage is between 1 and 2mm, far exceeding the allowable upper limit of 0.3mm. This type of damage is rare in previous projects. Due to the special repair parts of the lower beam, if the construction is carried out according to the conventional method, it is bound to knock down a large number of original intact front door beams, outer beams and panels and other large concrete components. After the partial beams are re-poured, the longitudinal beams, Panel and cast-in-place surface layer. This method greatly increases the repair cost and lengthens the construction period, and the on-site loading and unloading production will have a longer time to stop, which has a greater impact. If the steel bonding technology is used, it is difficult to construct according to the steel bonding technology because the location to be repaired and reinforced is in a special place. The use of carbon fiber to reinforce the concrete structure can make full use of its high strength and high elastic modulus to improve the bearing capacity and ductility of components, thereby reducing or reducing the impact on site loading and unloading during construction. Specifically, epoxy resin grout is used to infuse the cracks, and considering that the lower beam is in the water level fluctuation area, the grout is hydrophilic when the epoxy resin is configured. After the above-mentioned grouting, the concrete components can basically restore the original strength. At the same time, in order to enhance the local shear resistance, tensile strength and fatigue resistance of the structure, after the cracks are repaired by epoxy resin grout, the repaired components are further reinforced with double-layer carbon fiber cloth within the cracks. That is, in the crack range, a layer of carbon fiber cloth (length 2m) is first pasted on both sides and bottom of the beam along the length of the beam, and then a layer is pasted along the cross section of the beam, so as to achieve the reinforcement requirement of enhancing the structural bearing capacity.

After two times of static load tests on the repaired wharf, the test results show that the cracks of the components are controlled to a certain extent after the joints are filled and reinforced with carbon fiber cloth, and no cracks continue to expand. Under the vertical load, the beam has basically reached the original design bearing capacity after being strengthened, which meets the safe operation requirements of the 40t non-standard gantry crane.